1. Field of the Invention
The present invention relates to an interior-finishing material for use in automobiles, such as for headlinings, doors, or the like. More specifically, the present invention relates to an interior-finishing material that can be readily produced by the one-piece molding method, and that has excellent sound absorbing characteristics, resistance to deformation against heat, and moldability. Furthermore, the present invention relates to a method for producing an interior-finishing material for use in automobiles having the above-mentioned excellent properties.
2. Description of the Prior Art
Various interior-finishing materials for use in automobiles, such as headlinings, etc., have long been proposed and produced. Japanese Patent Publication No. 62-20003, for instance, discloses the following method for producing an interior-finishing material. First, fibers are bound with a thermoplastic resin or a mixture of a thermoplastic resin and a thermosetting resin, resulting in a sheet. The sheet (i.e., the substrate) is preheated to about 120.degree. C. and a surface material is attached thereon via a layer of a thermosetting adhesive that can be cured at a temperature of up to 120.degree. C., and the laminate is treated by cold compression molding. In this method, the substrate is heated at a relatively low temperature such as about 120.degree. C. so that the surface material does not deteriorate, as it would at high temperatures. However, the thermoplastic resin serving as a binder fails to melt thoroughly at such a low temperature. Therefore, the bindings between the fibers are not released satisfactorily. When the heated substrate is compression-molded, stress caused by the deformation of the substrate remains. Accordingly, when the molded article is kept at a high temperature, the molded article tends to return to its original shape. In this method, an adhesive layer is provided that is curable at the relatively low temperature of up to 120.degree. C. to help prevent deformation of the molded article caused by residual stress. However, the adhesive layer is very thin compared with the thickness of the substrate, resulting in insufficient prevention against the aforementioned deformation. When the thermosetting resin is incorporated into the substrate, the degree of the deformation is less than that of the substrate that contains only the thermoplastic resin. But even when the thermosetting resin is incorporated, a sufficient effect cannot be obtained. In particular, when the substrate is thick, the stress that arises in the substrate becomes large, resulting in more deformation.
Furthermore, in the method mentioned above, as the thermoplastic resin serving as a binder does not melt completely, the substrate is molded with the fibers being bound with the binder. When the substrate is press-molded, the flowability of the fibers is poor that compose the substrate is poor; that is, the fibers do not move easily. Therefore, it is difficult for the substrate to be accurately formed into the shape of a mold, and thus, greater pressure is needed for molding. Thus, the method has a drawback in that the molding process cannot be performed with accuracy.